Surface morphology of laser tracks used for forming the non-smooth biomimetic unit of 3Cr2W8V steel under different processing parameters

Aiming to form the high quality of non-smooth biomimetic unit, the influence of laser processing parameters (pulse energy, pulse duration, frequency and scanning speed in the present work) on the surface morphology of scanned tracks was studied based on the 3Cr2W8V die steel. The evolution of the surface morphology was explained according to the degree of melting and vaporization of surface material, and the trend of mean surface roughness and maximum peak-to-valley height. Cross-section morphology revealed the significant microstructural characteristic of the laser-treated zone used for forming the functional zone on the biomimetic surface. Results showed that the combination of pulse energy and pulse duration plays a major role in determining the local height difference on the irradiated surface and the occurrence of melting or vaporization. While frequency and scanning speed have a minor effect on the change of the surface morphology, acting mainly by the different overlapping amount and overlapping mode. The mechanisms behind these influences were discussed, and schematic drawings were introduced to describe the mechanisms.     

Structure,morphology, and growth dynamics of perfluoro‐pentacene thin films

We report high structural order in thin films of the organic semiconductor perfluoro‐pentacene (PFP), which is a candidate material for n‐type applications, deposited by vacuum sublimation on oxidized silicon wafers. Bragg reflections up to high order in both specular and grazing incidence geometries and a mosaicity of less than 0.01° demonstrate the well defined structure. The thin film entirely consists of crystallites with a structure close to the bulk phase without any contamination with a second phase. Real‐time X‐ray measurements show that PFP grows in a Stranski–Krastanov growth mode with the first monolayer wetting the substrate before 3d‐growth sets in during growth of the second monolayer. Implications for its use are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and morphology of Cu/Ni film grown by electrodeposition method: A study of neutron reflectivity and AFM

We present detailed study of structure and interface morphology of an electrodeposited Cu/Ni film using X-ray diffraction, X-ray reflectivity, neutron reflectivity and atomic force microscopy (AFM) techniques. The crystalline structure of the film has been determined by X-ray diffraction, which suggest polycrystalline growth of the film. The depth profile of density in the sample has been obtained from specular X-ray and neutron reflectivity measurements. AFM image of the air-film interface shows that the surface is covered by globular islands of different sizes. The AFM height distribution of the surface clearly shows two peaks and the relief structure (islands) on the surface in the film, which can be treated as a quasi-two-level random rough surface structure. We have demonstrated that the detailed morphology of air-film interfaces, the quasi-two-level surface structure as well as morphology of the buried interfaces can be obtained from off-specular neutron reflectivity data. AFM and off-specular neutron reflectivity measurements also show that the morphologies of electrodeposited surface is distinctively different as compared to that of sputter-deposited surfaces in the sample.     

Comparison of fractal analyses methods and fractal dimension for pre-treated stainless steel surfaces and the correlation to adhesive joint strength

The fractal dimensions of six differently mechanically pre-treated stainless steel samples were investigated using five fractal algorithms. The surfaces were analyzed using a profiler, atomic force microscopy (AFM), scanning electron microscopy (SEM) and light microscopy (LM), and thereafter adhesively bonded and tested in single-overlap joints to test their tensile strength. All samples showed different fractal behavior, depending on the microscopic methods and fractal algorithms. However, the overall relation between fractal dimension and tensile strength is qualitatively the same, except for the SEM images. This verifies that tensile strength is correlated to fractal dimension, although only within the length-scale of the profiler and the light microscope (≈0.5–100 μm). The AFM method was excluded in this comparison, since the limitation in the z-direction for the AFM scanner made it difficult to scan the rougher parts of the blasted samples. The magnitude of the surfaces is a parameter not often considered in fractal analysis. It is shown that the magnitude, for the Fourier method, is correlated to the arithmetic average difference, R_a, but only weakly to the fractal dimension. Hence, traditional parameters, such as R_a, tell us very little about the spatial distribution of the elevation data. Received: 22 December 1999 / Accepted: 9 October 2000 / Published online: 9 February 2001     

Sliding size distribution in a simple spring-block system with asperities

We use a simple spring-block system as a qualitative analogous of a seismic fault. The role of the asperities present in a real seismic fault is played by sandpapers of several grades. With this experimental array Gutenberg-Richter type-laws are obtained. We also observed that the maximum characteristic event in each experimental run depends on both the mass of the sliding blocks and the age of the sandpapers used at the interface between the blocks and the rough track.     

A Model for the Contact Angle of Liquid Droplets on Rough Surfaces

Up to now, measured results of the contact angle on rough surfaces have been explained usually based on the Wenzel equation （1936） and the Cassie-Baxter equation （1944）. However, these equations do not take into account considerations of liquid wetting behaviors on rough surfaces, and this leads to poor understanding of the mechanisms of contact between liquid droplets and rough surfaces （e.g. contact angle hysteresis）. We propose a new model for the contact angle of liquid droplets. By means of the present model, we can well understand the evperimental data which could not be well explained by the Wenzel equation and the Cassie-Baxter equation.     

Ni thin films vacuum-evaporated on polyethylene naphthalate substrates with and without the application of magnetic field

We study the structural properties of the surface roughness, the surface mound size and the interfacial structure in Ni thin films vacuum-deposited on polyethylene naphthalate (PEN) organic substrates with and without the application of magnetic field and discuss its feasibility of fabricating quantum cross (QC) devices. For Ni/PEN evaporated without the magnetic field, the surface roughness decreases from 1.3 nm to 0.69 nm and the surface mound size increases from 32 nm to 80 nm with the thickness increased to 41 nm. In contrast, for Ni/PEN evaporated in the magnetic field of 360 Oe, the surface roughness tends to slightly decrease from 1.3 nm to 1.1 nm and the surface mound size shows the almost constant value of 28-30 nm with the thickness increased to 35 nm. It can be also confirmed for each sample that there is no diffusion of Ni into the PEN layer, resulting in clear Ni/PEN interface and smooth Ni surface. Therefore, these experimental results indicate that Ni/PEN films can be expected as metal/insulator hybrid materials in QC devices, leading to novel high-density memory devices.     

Current-in-plane giant magnetoresistance: The effect of interface roughness and spin-depolarization due to the proximity of a buffer layer

We report on proximity effects of a Au buffer layer on the current-in-plane giant magnetoresistance effect (CIP-GMR) in high-quality, epitaxial Fe/Cr/Fe(001) trilayers. The lower Fe layer is grown in the shape of a wedge and allows simultaneous preparation of 24 GMR stripe-elements with different lower Fe thicknesses in the range from 13 to 14.5 ML. The layer-by-layer growth mode in combination with the small thickness variation gives rise to: (i) well-controlled roughness changes from stripe to stripe as confirmed by reflection high-energy electron diffraction (RHEED), and (ii) to a varying influence of the underlying Au buffer. The oscillatory roughness variation along the wedge yields an oscillatory GMR behavior as a function of Fe thickness and confirms the previous result that slightly increased interface roughness causes a higher GMR ratio. The proximity of the Au buffer to the GMR trilayer results in an increase of the GMR ratio with increasing Fe thickness. The latter effect is explained by spin-depolarization at the Fe/Au interface and in the bulk of the Au buffer.     

Reversible Vertical Manipulations of Single Pt Adatom on Pt（111） Surface with a Triple-Apex Tip

With a triple-apex tip, we investigate theoretically the vertical manipulation of single Pt adatom on the Pt（111） surface. The adatom adsorbed on the f cc site of the flat Pt（111） surface can be transferred vertically to the tip by adjusting the tip height properly. Moreover, based on the strong vertical trapping ability and the relatively weak lateral trapping ability of the tip, we propose a simple method to realize a reversible vertical manipulation of the Pt adatom from the highly coordinated sites, the kink and the step sites, of the stepped Pt（111） surface. All the vertical manipulations are completed using only the atomic force between the tip and the adatom, without the electric field.     

Origins of interdiffusion, crystallization and layer exchange in crystalline Al/amorphous Si layer systems

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250 °C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange.     

Surface electromagnetic radiation from a spatially modulated oscillating dipole layer

We present the calculation of surface electromagnetic radiation to all orders from a spatially modulated, oscillating dipole layer sandwiched between two dielectric media. The results properly include the macroscopic local field factors. In specular reflection direction, we show that the total radiation is partitioned into a term which is the zeroth-order counterpart to the higher-order diffraction and a term related only to the properties of two adjoining bulk media. The results unify the calculations by Shen and Heinz and McIntyre [1, 6, 7]     

Investigation of SiO2/Si3N4 films prepared on sapphire by r.f. magnetron reactive sputtering

Sapphire is a desired material for infrared-transmitting windows and domes because of its excellent optical and mechanical properties. However, its thermal shock resistance is limited by loss of compressive strength along the c-axis of the crystal with increasing temperature. In this paper, double layer films of SiO₂/Si₃N₄ were prepared on sapphire (α-Al₂O₃) by radio frequency magnetron reactive sputtering in order to increase both transmission and high temperature mechanical performance of infrared windows of sapphire. Composition and structure of each layer of the films were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. Surface morphology and roughness of coated and uncoated sapphire have been measured using a talysurf. Flexural strengths of sapphire sample uncoated and coated with SiO₂/Si₃N₄ have been studied by 3-point bending tests at different temperatures. The results show that SiO₂/Si₃N₄ films can improve the surface morphology and reduce the surface roughness of sapphire substrate. In addition, the designed SiO₂/Si₃N₄ films can increase the transmission of sapphire in mid-wave infrared and strengthen sapphire at high temperatures. Results for 3-point bending tests indicated that the SiO₂/Si₃N₄ films increased the flexural strength of c-axis sapphire by a factor of about 1.4 at 800 °C.     

Surface morphology of ZnO buffer layer and its effects on the growth of GaN films on Si substrates by magnetron sputtering

ZnO thin films were first prepared on Si(111) substrates using a radio frequency magnetron sputtering system. Then the as-grown ZnO films were annealed in oxygen ambient at temperatures of 700, 800, 900, and 1000°C , respectively. The morphologies of ZnO films were studied by an atom force microscope (AFM). Subsequently, GaN epilayers about 500 nm thick were deposited on the ZnO buffer layers. The GaN/ZnO films were annealed in NH₃ ambient at 900°C. The microstructure, morphology and optical properties of GaN films were studied by x-ray diffraction (XRD), AFM, scanning electron microscopy (SEM) and photoluminescence (PL). The results are shown, their properties having been investigated particularly as a function of the ZnO layers. For better growth of the GaN films, the optimal annealing temperature of the ZnO buffer layers was 900°C.     

Monte Carlo study of the step flow to island nucleation transition for close packed structures

Using joined super-lattice Kinetic Monte Carlo and continuous simulations we study the transition between step flow and two-dimensional island nucleation growth on stepped surfaces for close packed crystalline structures. The numerical analysis is performed in terms of misorientation cut, deposition rate and temperature. We compare the results of the atomistic approach with the predictions of the standard and generalized Burton-Cabrera-Frank (BCF) continuous model. The generalization consists in the explicit inclusion in the theory of the formation and dissolution of mobile dimers on the terraces. We show that the BCF-like continuous theories break down for low temperatures, large off-angle cuts and high deposition rates. In view of these results we critically discuss the basic assumptions of the continuous models.     

A model for vibrational properties of the atomic interface in A/B fcc metals

The motivation of this theoretical work is to introduce a model calculation for the elastic waves scattering and coherent phonon transport at an atomic nanojunction between face-centered cubic (fcc) leads. The model system A/B consists of two perfect semi-infinite fcc leads A and B, oriented in the same direction and joined by an atomic interface. It is applied to the system Cu/Ni and its inverse Ni/Cu. A theoretical approach based on the matching method is used to study the dynamics of the system A/B.     

Directional Nanoslit-Bump Coupler for Surface Plasmon Polaritons

We investigate a p-polarized plane wave transmitted through a metallic slit-bump nanostructure using the finite difference time domain simulation. It is found that narrow bumps with suitable separation can diffract surface plasmons into highly directional collimating beams. The number and directionality of the beams can be controlled by adjusting the geometry parameters of the nanostructure. The structure with optimized parameters may be interesting for practical applications as directional nanoslit SPP-light coupler in integrated photonic devices.     

Critical behavior of interacting surfaces with tension

Wetting phenomena, molecular protrusions of lipid bilayers and membrane stacks under lateral tension provide physical examples for interacting surfaces with tension. Such surfaces are studied theoretically using functional renormalization and Monte-Carlo simulations. The critical behavior arising from thermally-excited shape fluctuations is determined both for global quantities such as the mean separation of these surfaces and for local quantities such as the probabilities for local contacts. Received: 30 January 1998 / Accepted: 17 March 1998     

Chemical reaction of sputtered Cu film with PI modified by low energy reactive atomic beam

Polyimide (PMDA-ODA) surface was irradiated by low energy reactive atomic beam with energy 160-180 eV to enhance the adhesion with metal Cu film. O₂⁺ and N₂⁺ ions were irradiated at the fluence from 5 × 10¹⁵ to 1 × 10¹⁸ cm⁻². Wetting angle 78° of distilled deionized (DI) water for bare PI was greatly reduced down to 2-4° after critical ion flounce, and the surface energy was increased from 37 to 81.2 erg/cm. From the analysis of O 1s core-level XPS spectra, such improvement seemed to result from the increment of hydrophilic carbonyl oxygen content on modified PI surface. To see more carefully correlation of the peel strength with interfacial reaction between Cu and PI, flexible copper clad laminate with Cu (9 μm)/Cu (200 nm) on modified PI substrate (25 μm) was fabricated by successive sputtering and electroplating. Firstly, peel strength was measured by using t-test and it was largely increased from 0.2 to 0.5 kgf/cm for Ar⁺ only irradiated PI to 0.72-0.8 kgf/cm for O₂⁺ or N₂O⁺ irradiated PI. Chemical reaction at the interface was reasoned by analyzing C 1s, O 1s, N 1s, and Cu 2p core-level X-ray photoelectron spectroscopy over the as-cleaved Cu-side and PI side surface through depth profiling. From the C 1s spectra of cleaved Cu-side, by the electron transfer from Cu to carbonyl oxygen, carbonyl carbon atom became less positive and as a result shifted to lower binding energy not reaching the binding energy of C₂ and C₃. The binding energy shift of the peak C₄ as small as 1.7 eV indicates that carbonyl oxygen atoms were not completely broken. From the analysis of the O 1s spectra, it was found that new peak at 530.5 eV (O₃) was occurred and the increased area of the peak O₃ was almost the same with reduced area of the peak carbonyl oxygen peak O₁. Since there was no change in the relative intensity of ether oxygen (O₂) to carbonyl oxygen (O₁), and thus O₃ was believed to result from Cu oxide formation via a local bonding of Cu with carbonyl oxygen atoms. Moreover, from X-ray induced Auger emission spectra Cu LMM which was very sensitive to chemical bonding, Cu oxide or CuOC complex formation instead of CuNO complex was clearly identified by the observation of the peak at 570 eV at higher 2 eV than that of metal Cu. In conclusion, when Cu atoms were sputtered on modified PI by low energy ion beam irradiation, it can be suggested that two Cu atoms locally reacted with carbonyl oxygen in PMDA units and formed Cu⁺O⁻C complex linkage without being broken from carbon atoms and thus the chemically bound Cu was in the form of Cu₂O.     

Effect of Al content on the properties of Cr1−xAlxC films prepared by RF reactive magnetron sputtering

Cr_1−xAl_xC films were deposited on high-speed steel by RF reactive magnetron sputtering. In this study, we aimed to identify the effect of the Al content on the properties of Cr_1−xAl_xC films. We found that Cr_1−xAl_xC films exhibited a fine columnar grain microstructure with some special characteristics, such as high hardness of Hv 1426, a low friction coefficient of 0.29, and a large contact angle of 90° for x = 0.18. Furthermore, an increase in Al content resulted in a decrease in film hardness and an increase in contact angle. Moreover, on annealing at 923 K, the mechanical properties of the films improved and a dense protective film of complex Cr₂O₃ and Al₂O₃ oxides was formed on the surface for better wear resistance, which will ultimately increase the lifetime of the high-speed steel substrate.     

Interaction of endothelial cells with biodegradable strontium-doped calcium polyphosphate for bone tissue engineering

Angiogenesis is of great importance in bone tissue engineering, and has gained large attention in the recent 10 years. However, little research has been done on the effect of biodegradable materials, especially their degradation products on the angiogenesis process. Strontium-doped calcium polyphosphate (SCPP) has been proved to be able to promote osteoblasts growth in vitro before. In the present work, the interaction of endothelial cells (ECs) with the scaffold of SCPP was investigated to evaluate its potential influences on angiogenesis. The cell adhesion on SCPP scaffold as well as the angiogenic behaviors including proliferation, migration and tube-like structure (TLS) formation of ECs treated by its degradation products was tested. The results were compared with those of CPP group and physiological saline (negative control). As the results showed, the surface of SCPP could promote the adhesion and spreading of ECs. Ca²⁺ and Pi as well as Sr²⁺ were the main degradation products of SCPP. They did not inhibit but could promote the proliferation of ECs within 90 days. Moreover, they could induce the migration and TLS formation of ECs. Since SCPP bears the ability to improve the adhesion and angiogenic behaviors of endothelial cells, it might benefit angiogenesis and serve as a more promising scaffold for bone tissue engineering application. Besides, this work may provide a new method for in vitro evaluation of biodegradable materials’ potential effects on angiogenesis.